A whipstock may generally refer to a device inserted in a wellbore that is used for deflecting a drill bit or mill in a direction that is angularly offset with respect to the orientation of the original wellbore so as to establish a new or additional drilling course. In most instances, a whipstock procedure involves setting an anchor and providing an angled whipstock surface supported by the anchor at the desired depth in the wellbore to conduct side track or lateral directional drilling operations through the casing string.
It is frequently desired to cut or mill a window in a casing string that also includes therein a smaller diameter tubular string, such as for conducting wellbore fluids, that terminates at a position above the desired position of the window. It has typically been necessary to first remove the tubular string from the wellbore prior to performing the whipstock operation. Removal of the tubular string requires considerable rig time and expense, but is required to permit the entry of a full-bore whipstock assembly into the casing for positioning at the desired depth for then milling or cutting a window in the casing.
The face of the whipstock is oriented to position the casing window at a desired radial azimuth relative to the borehole axis in accordance with the new course of drilling. With the casing window properly positioned, the side track or lateral drilling operation may proceed in the desired azimuthal direction relative to the borehole. The face of the whipstock may be oriented using a multiple trip operation into and out of the wellbore.
The setting of anchors and whipstocks for purposes of milling windows in the casing string has been performed for many years. However, apparatus and methods have not heretofore existed that permit milling a window in the casing string by passage of a retrievable whipstock assembly through a smaller diameter tubular member, such as a production tubing string positioned within the casing. As well, more reliable apparatus and methods are desired for setting an anchor and a whipstock assembly within a casing positioned downhole by passing through a smaller diameter tubular member, such as a production string.
Consequently, there remains a need for apparatus and methods that offer the drilling industry the flexibility to reduce drilling time and costs by allowing installation and removal of a whipstock assembly at a desired position in the casing, and for reliably setting a whipstock assembly passed through a smaller diameter tubular member. Those skilled in the art have long sought and will appreciate the present invention which provides solutions to these and other problems.